Understanding Society User Support

Dear Support Team,
I aim to derive for each women the birth year, age and birth order of all her child ever had i.e., even before the start of the panel. I would like to do this for both BHPS and UKHLS, although I can use them as cross-sectional, so that it is not necessary to keep the corresponding hhorig values to link the two panels.

However, for my understandings, in both panels does not exist a variable showing the total number of child an individual have had (in UKHLS there's nchild_dv, but it refers to how many children in the household). So, is it necessary to derive it?
Furthermore, to link the birth year and age of child to the corresponding mothers, I can both use INDALL with mndip or INDALL + EGOALT exploiting the relationship (correct?). But in this case, I cannot observe all possible child, so I need to use also the NATCHILD file and the lchdoby variable, right? But what about the BHPS? I cannot find a way to identify all possible children/birth ever had, as it seems there's no information about the non-resident births.

Lastly, I wonder why there are so many inapplicable cases in the newborn file. How can I identify a "birth-event" if there are so many inapplicable cases with no information about year of birth of the supposed new-birth?

Many thanks for your support!

Luca Giangregorio